1. Field of the Invention
The present invention relates to the general field of heating apparatus, such as stoves for cooking. More specifically, it concerns a stove that combines cooking with a combustion source of heat such as coal and very high efficiency in doing so. In fact, the efficiency is so high that consumption of coal in the invention is a little more than half of that in prior art coal fired stoves. The invention is further distinguished from prior art coal fired stoves by being portable and cool enough to hold with bare hands. The efficiency and cool outer surface both result from a double walled exterior structure through which all combustion air is ingested.
2. Description of the Prior Art
The art and science of cooking goes back many thousands of years. Art work by cavemen shows knowledge of cooking with fire. When coal was discovered, a highly concentrated combustible fuel source that provided very high temperatures with slow fuel consumption became available. Over time, it was learned that using coal for cooking dictated construction of cooking apparatus from materials that could withstand high temperatures, such as iron and steel.
But iron and steel have two significant drawbacks when viewed in the context of the present invention. First of all, they readily absorb radiated and conducted heat, and in turn radiate that heat to the ambient atmosphere. Second, they make the cooking apparatus very heavy. The result is significant wasteful loss of heat that is intended for cooking, and essentially no portability.
It is well known that hot air is less dense than cold air. This causes hot air such as created by a combustion source to rise. In a closed structure containing a heat source and having openings at the bottom and at the top, a tower of rising air is created. This phenomenon is known as the chimney effect.
Another well known physical principle is that the velocity of a gas such as air passing through a walled structure such as a cylinder increases as the cross section of the structure decreases. Thus if the structure is a cylinder, as its diameter decreases, the velocity of the air increases. The presence of a throat, or narrowed cross section, creates what is known as a venturi.
It is known in the prior art to make heat containing structures with a double walled construction. Two examples of that are U.S. Pat. Nos. 6,761,160 and 5,203,316. The latter is a double walled oven. Once, the double walled construction was in part done to make the outer wall cooler to the touch, U.S. Pat. No. 5,921,229. But so far as is currently known to the present inventors, the combination of chimney effect, a venturi, and a double walled construction has never been employed in a stove to increase the efficiency of the heating or cooking. Efficiency is increased because the combustion chamber is surrounded by a double walled structure through which all the combustion air moves, preheating it, and preventing the loss of nearly all the heat from escaping laterally. Rather nearly all heat generated by combustion is radiated to the bottom of the cooking pot or exhausted along the pot's walls to heat it by conduction.